Polymers are a mainstay of modern society, for example, widely used in fabricating textiles, upholstery, construction materials, various air, land or sea vehicles, and microelectronic devices and appliances. The inherent flammability of many polymers poses a significant threat, especially in enclosed or isolated spaces. Therefore, as synthetic polymers are used extensively in society as plastics, rubbers, and textiles, polymer flammability has been recognized as a safety hazard and remains an important challenge in polymer research.
Fire or flame retardant (FR) additives may be used to temper polymer flammability. For example, brominated organic compounds comprise a large subset of FRs used today. Flame retardants are incorporated into polymer materials as small molecule additives, or as part of the polymer backbone, to reduce flammability. A number of halogenated molecules, including aromatic and aliphatic brominated compounds, have been employed to reduce polymer flammability. Brominated aromatic flame retardants can be found in a wide-range of products, including computer, textiles, foam furniture, and construction materials.
FR compounds also face legislative scrutiny due to health and environmental concerns, particularly related to bioaccumulation (e.g., polybrominated diphenyl ether (PBDE) has been detected in umbilical cord serum and breast milk). (See, U.S. Senate CPSC Reform Act of 2007 (S.2045) (US Senate Bill 3616); Gomara et al., Environ Sci Technol 2007; 41: 6961-6968.); Blum et al., Science 1977, 195: 17-23; Gold et al. Science 1978; 200: 785-787).
The environmental accumulation of halogenated flame retardants raises concerns that are restricting their use, and requires the development of nonhalogenated alternatives. In addition, some halogenated flame retardants release hydrogen halide gas upon combustion, which is especially undesirable in confined spaces, such as on aircrafts and ships. These concerns have led to an emphasis on non-halogenated flame retardants in recent years. However, non-halogenated flame retardant additives, such as alumina trihydrate, compromise the physical and mechanical properties of polymers when loaded at high levels.
Accordingly, there remains an urgent, on-going need polymers and for a general synthetic strategy toward a broad range of structurally and functionally diverse flame-retardant polymers.